In the past three years, seven system development projects involving industrial and academic partners have been carried out within Centre for Object Technology. Central to all projects has been an intensive use of a diversity of object-oriented tools and techniques. Based on the experiences from the projects, we discuss tool support for central activities in iterative development and point to directions for future research in development of usable object-oriented tools. Even though a variety of different (CASE) tools can collectively support an iterative, object-oriented system development process, we argue that there is a need for a deeper understanding of, and a better support for, concrete activities in system development practice. Furthermore, there is and cannot be a perfect tool for iterative object-oriented system development: tool developers also need to focus on the art- and skilful interplay and integration of separate tools.